Method of flexible heating in intermittently operable systems



July 28, 1942. c. H. BUCK 2,291

METHOD OF FLEXIBLE HEATING IN INTERMITTENTLY OPERABLE SYSTEMS FiledApril 13, 1940 I I I I l PI|3 2 F 1 .3 W

''7 .SLI'P FRICTION 5 CONNECT/0 INVENTOR. "a5 35 54 37 /m5; /7. 506K.

Patented July 28, 1942 UNETED STATES PATENT OFFICE METHOD OF FLEXIBLEHEATING IN INTER- MITTENTLY OPERABLE SYSTEMS 1 Claim.

This invention relates to means for and a methd of obtaining what isgenerally known as flexible firing effect from an intermittentlyoperable combustion source.

The chief object of this invention is as suggested above, to-wit; toprovide means for an intermittently operable combustion source and to socontrol the operation of said combustion source and the heattransferring medium and means that a flexible firing effect is obtainedfrom an installationof the intermittent type.

The chief feature of the invention consists in operating such anintermittent combustion source and controlling the medium and meansassociated therewith so that when heat is desired for household or likheating purposes, as soon as the combustion source produces an initialamount of heat, the heat transferring medium is initially circulated andat a lower rate than at the rate which is utilized when the combustionsource is operating at maximum capacity and the transfer of heat isbeing rapidly effected, coupled with the further provision that whenheat is no longer demanded for such household heating, the heat storedin a portion of the heat transferring mechanism is slowly dissipatedinto the heat transferring medium as distinguished from the present andprior practice of rapidly transferring the same with the result that theeffect of flexible firing is obtained and with the further result thathigh over-run operation is either very materially reduced orsubstantially eliminated.

For a complete understanding of the invention, it should be noted thatfor household heating there is generally provided one or more roomthermostats in the desired location or locations, each of which isadapted to control the combustion source. This combustion source may bea gas fired furnace, an oil fired furnace, or a stoker fed furnace, asapplied to hot air heating. If applied to hot water or steam heating,the same type of fuel may be utilized. Since the problems sought to besolved by this invention and solved thereby are more particularly acutein hot air heating installations, the following description and thedrawing describe and illustrate, respectively, a hot air embodiment ofthe invention. In hot air heating, the same may be of two types; thegravity type or the forced warm air type. In connection with the gravitytype, it is Well known that when the intermittently operable combustionsource supplies heat that the air in contact with the bonnet and thelike and included as a part of the circulating system for the airmedium, immediately becomes heated and to a corresponding proportionaldegree and immediately starts to circulate and as the source of heatsupplies additional heat to the bonnet, the rate of the circulationincreases.

Then when the thermostat opens the circuit controlling the heat source,the heat previously stored in the bonnet and the like continues todissipate or transfer to the circulating air in a decreasing amount ofheat following cessation of heat supplied to the bonnet, until the heatis exhausted from the bonnet, whereupon the circulating medium, the air,ceases circulation.

It has been ascertained that the public is demanding clean heatingequipment with the result that the circulation of air as aforesaidrequires cleaning of the air which may be of two characters, either bywashing or by filtering. Washing of the air is needlessly expensive.Filtering of the air is relatively inexpensive and practically all hotair installations, at the present time, are of the forced Warm aircharacter'for the reason that the filter arrangement, when introducedinto the gravity type system, practically prohibits gravity flow.Consequently, the necessity for filtering being paramount, there isprovided a means for positively circulating the air in the system. Inalmost all instances, the cold air return discharges to a filterarrangement and a fan or blower draws the cold air through thefilters'which are replaceable and then forces the filtered air aroundand over the bonnet and other heating surfaces of the combustion source,and thence into the several pipes leading into the rooms to be heated.

The present invention is applied to th last mentioned type of system,although modifications thereof may be applied to other types of systemspreviously mentioned, with but slight change.

The present invention contemplates the utilization of a multi-speedmotor for operating a fan or blower and, preferably, the motor has twospeedsthe high and the low speed. The household room thermostat is themaster control. When heat is required, it, through appropriate controlmeans, insures the initiation of heat supply to the bonnet byautomatically opening the gas valve in a gas fired furnace, etc.

The types of fuel are solid, liquid or vapor, to-wit: coal or coke, oilor gas. Usually there is no forced supply of air for a gas unit. Thereis a forced supply of air for oil and solid fuel consuming units.Generally, this forced supply of air is operated simultaneously withfuel supply. The fuel supply proper, as well as the air supply, iscustomarily provided with a safety arrangement which, in the event thatcombustion cannot take place or does not occur, the fuel and air supply,while initiated, immediately ceases to function. This is the safety orprotective factor which is standard in all intermittently operablecombustion sources, more especially in gas and oil fired arrangements,but is also included in solid fuel fired arrangements in that unless thesolid fuel initially supplied does not immediately continue to burn andto the desired amount, a thermally responsive element immediately cutsoff continued fuel and air supply so that such solid fuel arrangementdoes not continue operation without combustion occurring simultaneouslytherewith. Since these types of controls and safety elements arestandard equipment, as stated, no further detailed description nor anyspecific illustration thereof is believed necessary.

Also, old and well known is the operation which follows: When the roomthermostat no longer calls for heat, the respective motors or controlsare deenergized or rendered inoperative and further fuel and air supplyis discontinued.

In such operation, it will be noted that for some interval followinginitial combustion the heat produced initially must heat all of theadjacent and surrounding parts in the combustion chamber, bonnet, etc.Thus, these types of heat sources differ from the more flexible typewherein there is resident as in a hand fired furnace a relatively largebody of fuel, that is relatively slowly burning at all times. The lattertype of construction is what is generally considered a flexible supply.

Returning to the intermittent type, following the initial heating of theparts in the combustion chamber which sometimes, particularly in gas andoil fired furnaces, includes heat absorbing refractories are employed toradiate heat combustion and such refractories have a heat absorbingcapacity th aforesaid must be satisfied before the bonnet is incondition to supply heat to the air adjacent thereto.

Following satisfaction of this condition, additional heat then must besupplied to raise the bonnet temperature until such time as the heattherein is sufficient to heat the air in contact with the bonnet and thelike, so that when the air is sumciently heated it can be circulated forheating purposes. It is customary in installations of this charactertoprovide a bonnet thermostat which, when the bonnet attains a certaintemperature, say for example 125 to 165, a circuit is closed by thatthermostat and through the fan motor which insures positive circulationof the heated air.

It will thus be noted that from the time the combustion source starts tosupply heat until the time that heat is adequately supplied to thecirculating air, there is an appreciable time lag. Then, it is evidentthat as long as the room thermostat calls for heat, the combustionsource will supply heat. When the room thermostat is thermally actuatedto open the control circuit to the combustion source, no further heat issupplied by that combustion source, or more particularly, the primarysupply.

, However, there is a large amount of heat stored in the bonnet andrefractories which, upon cessation of combustion, still is in conditionto discharge and transfer heat so that long after the room thermostatshuts off, the bonnet thermostat still holds the circulating fan motorcircuit closed until such time as the bonnet thermostat opens thatcircuit incident to the cooling of the bonnet by reason of the forcedcirculation of the cooler air from the several rooms to and over thebonnet and back to said rooms.

The resulting condition is this. If the thermostat is set, for example,to supply heat at a predetermined temperature and is adjusted to out offheat supply at several degrees thereabove, this so-called intermittentheating results in what is known as a "high over-run and this is becausethe bonnet thermostat continues fan operation. The resulting action inthe rooms to be heated is that there is at each cycle a relatively widefluctuation between the actual room temperature when heat is supplied inresponse to room thermostat demand for heat and the final roomtemperature effected, long after the room thermostat has been satisfied.These are always considerably below and above the temperatures for whichthe room thermostat demands or causes a cessation of operation at theprimary source.

Insofar as forced feed hot air heating is concerned, therefore, theproblem is emphasized many times when such heating system is associatedwith an intermittently operable source of heat.

The present invention contemplates the employment of a multi-speed motorfor the air circulating fan or blower and having the former socontrolled that when the primary heat source is conditioned to supplyheat and is not otherwise inoperable, the fan motor shortly after suchconditioning, operates at low speed and then when the bonnet temperatureincreases to the proper amount the low speed motor operation isdiscontinued and high speed motor operation of the fan is effected whichis continued so lon as the room thermostat calls for heat.

Immediately upon the room thermostat shutting off, the air circulatingfan motor, or rather shortly thereafter, ceases to operate at highspeed, but is then operated at low speed and this low speed operation iscontinued until the bonnet temperature has sufiiciently decreasedwhereupon cessation of all forced feeding of air is effected.

From the foregoing, therefore, it will be understood that during thefire build-up period and during the fire dying period, corresponding toa hand-fired furnace, the air circulating fan mo tor operates at slowspeed while during the maximum or full draft period of a comparable handfired furnace, the air circulatin fan motor operates at high speed.Thus, there is obtained with this invention that condition comparable toa flexible firing effect by utilizing as a primary source of heat, anintermittently operable combustion source.

The objective result is that the so-called high over-run heretoforeinherent in intermittently operable combustion source systems, togetherwith other inherent difliculties or objections are eliminated.

One of the latter is the elimination of so-called air stratificationcommon to such intermittently operable systems and not generallypresent, unless there is an air locking or binding, in a gravity system.It may be noted, also, that when the latter condition occurs in agravity system, practically the only solution to that problem is toapply a forced circulating arrangement by installing a fan or blower topositively insure proper circulation.

The basic invention, therefore, it will be appreciated from theforegoing, relates primarily to the cycle of control for obtainingflexible firing effect from an intermittently operable combustionsource. Certain phases of the invention are equally advantageouslyapplicable to certain other types of combustion sources, such as thoseknown as high-low firing systems and those known as flexible flamefiring systems, although specific mention hereof of the same is not tobe construed as excluding others to which the present invention mightalso be applied with the same advantages attendant upon suchapplication.

The problems inherent in heating system contructions are well/known andattempts have been made to solve the same by utilizing time controlswhich have definite time factor applications, regardless of thetemperature difference between the interior of the house to be heatedand the exterior, so that such time controls, while seeking toaccomplish substantially the same objective, to-wit: the solution ofthese problems fail to accomplish the same over a wide range ofconditions because the adjustments must be so made that they only applyto the average temperature difference condition.

The present invention, therefore is universally flexible since, as willbe hereinafter pointed out more fully, it operates solely upontemperature difference and, therefore, regardless of the temperaturedifference between the interior of the house to be heated and theexterior or outside air, the system always properly functions and theproblems previously inherent in intermittently operated combustionsources, time lag responsive control systems are not present.

Having thus described the cycle of operations, the problem and thesolution effected by such cycling reference will now be had moreparticularly to apparatus capable of effecting such cycling.

It is to be understood, however, that while the several parts of thisapparatus are illustrated as of mercury switch character they may be ofsnap switch character or of relay switch type. Mercury switches arenotoriously effective and safe, the circuit being made and broken withina sealed chamber, thereby reducing fire hazard to a minimum hence thepreferred form of the ap paratus invention is illustrated and describedas including mercury switches.

The full nature of the invention will be understood from theaccompanying drawing, the following description and claim:

In the drawing, Fig. 1 is a diagrammatic sectional view through a forcedair heating system including the invention applied thereto, the latterbeing more or less illustrated diagrammatically.

Fig. 2 is a wiring diagram of connections showing mercury switchapplications throughout.

Fig. 3 is a diagram of a warp switch modification of a portion of theswitching arrangement shown in Fig. 2.

Fig. 4 is a perspective view of a temperature responsive switcharrangement.

In Fig. 1 of the drawing, there is indicated a combustion chamber I 0surrounding a bonnet H, in turn surrounded by the furnace casing l2,

the other ends of which are connectedto registers and the like by coldair ducts. These registers are positioned, usually, in the floor of oneor more rooms in the lower floor of a multi-floor building. Therelatively cool air entering the intake ll passes through thesuper-heater and is initially heated. It then passes through the filterstructures l8 being drawn therethrough by a fan structure l9 hereinshown belt-driven as by the belt 20 from the fan motor 2| which,preferably, is of multi-speed character. This arrangement, however, canbe direct drive or can be two motors with slip clutches, if desired. Thefan discharges as at 22 to the chamber between the outer part of thefurnace and the dome and bonnet arrangement.

The hot air discharges from the furnace by one or more outlets 23 which,through suitable conduits, discharge to the several rooms. Theseconduits usually are valve controlled.

Associated with the bonnet and dome is what might be termed the bonnetswitch, herein designated by the letter A. Also carried externally ofthe furnace proper is another motor controller arrangement 24 to whichreference will be had hereinafter.

The present form of the invention illustrated includes a tubularstructure 25 adapted to supply both air and oil to the combustionchamber [0 and this air and oil is supplied by a combination unitincluding a motor and fan arrangement, together with all the customarysafety devices, valves and pipe, and the same is designated generally bythe numeral 26 in Fig. 1.

Reference will now be had to Fig. 2. Herein is illustrated the powersupply mains 38 and 3|. In the event the room thermostat 32 is of voltcharacter, it is included in series for direct control and operation ofthe controller arrangement 24 which, as before stated, controls the airand fuel supply motor combination 26. As long as this thermostat 32 isclosed, air and fuel will be supplied for combustion purposes, providingthe controller 24 is properly conditioned.

Usually the controller 24 includes a safety device which prevents thesupply of fuel if the device is not conditioned for proper operation.

Herein line 33 includes a supply line to the controller 24 and line 34includes the return. It, of course, is obvious that the thermostatswitch may be of a remote control character, that is, close a switchthat in turn controls the supply of energy that is supplied to thecontroller mechanism included in the controller 24.

Furthermore, it is quite apparent that the room thermostat in the latterinstance also may be of low voltage type and then would derive itsvoltage supply from a small transformer. All of these are conventionalvariations and are well known in standard practice.

In Fig. 2, the motor 2| is provided with terminals 35, 36 and 31. Theterminal 38 is connected by line 38 to one of the mains, which is theground main. The motor is so arranged that when cur rent is supplied toterminal 35, the motor operates at high speed, and when current issupplied to terminal 31 the motor operates at low speed. Thus, the fanoperates at high or low speed, respectively, depending upon to whichmotor terminal current is supplied.

Included in the dotted lines indicated by the letter A in Fig. 2, is thebonnet switch and included within the dotted lines B in Fig. 2, is thestack switch.

Since certain of the parts hereinafter to be described, are conventionaland well known coristructions, only briefreference'willbe had thereto.For example,incorporated as'a partof the stack switch is a bi-metallichelix 39, which upon being s'ufficiently heated has 'one' end arrangedto cause rotational movement. This rotating end is indicated by thenumeral 40'an'd carries a support 4| that is tiltable clockwise. andanticlockwise to certain stops which limit the extent of the movement,regardless of the changes of temperature.

Carried by the'member 4| is a single pole double throw mercury 'tube'switch indicatedgenerally by the numeral 42 and included therein is a'central terminal 43 andtwo oppositely directed contact terminals 44 and45. Extending into each end of the tube is a contact member such as 46and 41. The mercury 48 is adapted to bridge alternately the switchcontacts 45 and 41 and 44 and 46, depending upon the position of themember 4|.

The member 4| also mounts another mercury switch indicated generally bythe numeral 49 and including mercury 50 therein and having two terminalsand 52 at one end. As shown in Fig. 2, which represents the dormantcondition, the mercury 50 in switch 49 does not close the circuit acrossthe contacts 5| and 52 and the mercury 48 in the other switch 42 doesnot close the circuit across the contacts 44 and, but does close thecircuit across the contacts 45 and 41. V

When there is an increase in temperature inthe stack incident to initialcombustion and long prior to any appreciable rise in temperature towhich the bonnet switch arrangement A is susceptible, the helix 39 isaffected and the member 4| is tilted, counter-clockwise; so as toclosethe circuit across contacts 5| and 52 in switch 49 and across 44 and 46in switch 42, and simultaneously open the circuitacross 45 and 41 in thelast mentioned switch.

These are the two positions assumed by this switch arrangement. The lastmentioned is what might be termed, active combustion position, and theformer, as shown in the drawing, is the so-called dormant position. Itis to be understood that the helix 39 is operatively connected tothemember 4|] such that there is a slip engagement connection effectedso that member 4| is operated by metal helix 39 on a change intemperature of a predetermined amount, regardless of the starting orstopping points of the structure.

Since this helix and its slip connection to a switch carrier is wellknown in the heating and ventilating control art, no specificdescription is believed necessary.

The bonnet switch structure A, see Figs. 2 and 4, includes a mercuryswitch 53 which at opposite ends includes a contact 54 and 55. Adjacenteach contact is a contact 56 and 51, respectively the two latter beingconnected together and hav. ing a common terminal connection 58. Themercury 59 in the tube is adapted to close the circuit across thecontacts 51 and 55 when the bonnet switch structure is in the inactiveor fire build-up position. The tiltable member 60 supports said switch53. It also supports another mercury switch 6| which at one end has twoterminals 62 and 63. The mercury 64 in said mercury switch is adapted,during the active combustion period or after the fire has been built upsufl'iciently to close the' circuit across contacts 62 and 63. Anelement similar to element 39 and indicated by the numeral 65 is exposedor responsive to bonnet temperatures. This switch arrangement A is ofthe slowacting type as compared to the switch B. This switch arrangementA is not of the slip charac ter whereas switch arrangement B is of thatcharacter so that as the bonnet temperature gradually rises, the member60 will gradually rotate counter-clockwise so that the circuit will beclosed across contacts 54 and 56 and across contacts 82 and 63 and willbe opened across contacts 55 and 51.

This tilted position of the bonnet switch in the counter-clockwisedirection is. maintained from the time that the switch becomesoperative, that is, responds to an increase in bonnet temperaturesufficient to cause the switches to be tilted, until such time as thetemperature of the bonnet drops. This, as previously set forth, occurs aconsiderable period after the fuel supply has been rendered inoperativebythe room thermostat due to thestorage of heat as before set forth. a

A line 10 connects the main 30 to the switch contact 62. The line 1|connects that same switch contact to the switch contact 5|. The line 12connects switch contact 52 to switch contact 63 and the line 1-2 is alsoconnected by line 13 to the common switch terminal 43 of the switch 42.The switch contact 41 is connected by line 14 to the terminal 31 or lowspeed terminal of the motor 2|. The line 15 also connects thereto and toth'e switch contact 55 in the switch 53. The switch contact 54 in theswitch 53 is connected by line 16 to the terminal 35 or the high speedterminal of the motor 2 The terminal 46 of switch 42 is connected byline 11 to the common terminal 58 of the mercury switch 53. In Fig. 2stops S limit the actual throw of the switch carrier 40. However, thespring 4|a permits the bi-metallic helix 39 to coil and uncoil asrequired by temperature conditions and there is thus insured properswitch carrier'movement in the ranges permitted by said stops S.

Having thus described the various connections, the circuits will be setforth briefly as follows:

When the room thermostat 32 calls for heat, the control 24 is suitablyenergized as before described. After a very slight interval, it will beobvious that the products of combustion escape through the smoke pipeand in so doing the temperature in the smoke pipe increases. When apredetermined amount of temperature difference has been obtained, member39 responsive to such temperature, responds thereto whichtilts themercury switches 42 and 49 counter-clockwise. In so doing, it will benoted that current then is supplied to low speed motor terminal 31 asfollows:

Current from the main 30 is supplied by line 10 to line 1| to theterminal 5| through the mercury 59 to the terminal 52 and thence by wayof lines 12 and 13 to the common terminal 43, thence by contact 44through the mercury 48 of switch 42 to the terminal 46, thence by line11 to the common terminal 58 of the switch 53 through the contact 51 andmercury 59 to contact 55 and thence by line 15 and 14 to the low speedterminal 31.

Thus, until the stack switch structure B has responded to apredetermined temperature in the stack, the fan motor 2| is notenergized even after the cycle has been initiated by the room thermostat32, but upon attainment of that predetermined temperature difference thelow speed portion of the motor 2| is energized for low speed fanoperation, thereby insuring relatively slow speed forced air operation.This is during the fire build-up period and before the bonnet hasattained a sufliciently high temperature to cause rapid circulation ofthe air.

When the bonnet has been sufiiciently heated the bi-metallic helix 65 ofswitch A becomes operative to rotate member 60 counter-clockwise so asto tilt the mercury switches 6| and 53.

When this occurs, the circuit is as follows:

The current is again supplied from line 38 by means of line I toterminal 62. The mercury 64 in switch 6| then bridges the contacts 62and 63 so that if current is supplied to line I2 and by mercury 50 tocontact 5| and thence to line II it is carried back to the contact 62.It will be noted that this in effect has no circuit effect, but thisfalse circuit condition is pointed out so that the real circuitcondition arrangement will be understood.

Current from line I0, as stated, through the mercury 64 passes fromterminal 62 to terminal 63 of switch 6| and thence by lines I2 and I3,it passes to the common terminal 43 of switch 42 and the mercury 48therein bridges contacts 44 and 46 completing the circuit to line 11connected to the common terminal 58. The mercury 59 in the switch 53 nowcompletes the circuit across the contacts 54 and 56 so that the line I6is in series with the line I0 so that current is supplied to motor 2|through the high speed terminal 35 for high speed operation of themotor. Therefore, high speed operation of the fan I9 insures rapidcirculation of the heated air between the bonnet and dome and thefurnace casting wall. This condition or circuit arrangement ismaintained as long as the control 24 is energized combustion continuesin the firebowl.

It is to be noted th'at if, for any reason, the control 24 fails tofunction due to mechanical or other failure when the room thermostatcalls for heat, the switch arrangement B does not function. Therefore nooperation of the fan motor occurs upon combustion source failure.

When the room thermostat responds to the heated condition caused by theoperation of the heating system being activated, it opens the circuit tothe control 24 and combustion ceases.

Within a relatively short time following such cessation of combustion,the bi-metallic helix 39 again becomes operative but in a reversedirection and upon the predetermined temperature drop the switches 42and 49 are tilted clockwise from their previous counter-clockwise tiltedposition. In so doing, the circuits are conditioned through these twoswitches as shown in Fig. 2.

It is, however, to be noted that due to the residual heat in the bonnet,firebowl, refractories, etc., the switch structure A is not positionedas shown in Fig. 2 but remains positioned in the tilted position as lastdescribed. The circuits then are as follows: Current is supplied by line30 to line I0 to contact switch 62 of switch 6| and since the mercury 50is now remote from the two switch points 5| and 52 of switch 49, nocircuit is completed through the switch 49 by line H The circuit,however, is completed by the mercury 64 across contact 62 and 63 andthence by lines I2 and I3 to the common switch terminal 43 of the switch42.

The mercury 48 now bridges the two contacts 45 and 41 so that current issupplied by line I4 from contact 41 to the low speed terminal 31 andthus substantially upon cessation of combustion or following the same,at a very short interval, air circulating fan high speed motor operationceases and low speed motor operation thereof occurs. This continuesuntil the bonnet temperature has dropped sufliciently so thatbi-metallic helix 65 again becomes operative in the opposite directionin an amount sufficient, to tilt the switches 6| and 53 clockwise to theposition shown in Fig. 2. Thereupon, since both switches 6| and 49 arein the clockwise tilted or dormant position, as shown in Fig. 2, nocurrent is supplied to either the high or low speed terminals 35 or 3!of the motor.

Reference will now be had to Fig. 3. In said figure there is indicated aheating device I09 supplied by lines |0| and I02 and these lines areconnected to the electrical power supply and are responsive to theoperative condition of the controller 24 and associated mechanisms. Inother words, if proper combustion cannot be eifected when the thermostat32 calls for heat, this heating element I 00 will not be energized forheating purposes or heated, at least if there be a safety controlincorporated in the controller 24, to such degree as to effect thermallya thermally responsive element, to-wit: a warp switch controller. Thiswarp switch controller is diagrammatically indicated in Fig. 3 as abi-metallic warp switch I03 mounted at I04 connected to a line I05which, in effect, is the line I3 in Fig. 2.

The bi-metallic warp switch member I03 is positioned between thecontacts I06 and- IM which are comparable respectively to switchcontacts 46 and 41 respectively of switch 42. A line from contact I0'Iindicated by numeral I08 is the same as the line I4 of Fig. 2 and leadsto the low speed terminal 31. A line I09 from contact I 06 is the sameas line 71 of Fig. 2 to common terminal 58 of switch 53.

As shown in Fig. 3, member I03 contacts the contact I01 and this is thedormant position. Upon the predetermined temperature differenceoccurring incident to the operation of the heating means I00 asbeforementioned, member I03 moves counter-clockwise and contacts thecontact I06. The bi-metallic strip I03 supports in insulated relation asat I III, a bridging contact member III adapted to contact two contactsH2 and H3 to which is connected lines I I4 and I I5. The contacts I I2and I I3 correspond to the switch points 5| and 52 of switch 49 in Fig.2 and the lines II4 and'II5 thereto and therefrom correspond to thelines 'II and I2 respectively, of Fig. 2.

The operation of this switch structure shown in Fig. 3 is functionallyidentical to that illustrated in Fig. 2 and represented therein anddesignated as the stack switch B.

In this connection, it should be noted that thc switch arrangement shownin Fig. 3 does not require that the switch arrangement be subjected tostack temperature differences or the like. In other words the basicinvention comprehends a switch arrangement which is responsive tocombustion per so, that is, switch B or the switch arrangement shown inFig. 3, tilts counterclockwise when combustion starts or shortlythereafter and when combustion stops or shortly thereafter this switcharrangement is tilted in the reverse direction.

Other electrically operable means may be utilized in lieu of either ofthe two specific switch arrangements disclosed herein.

While the invention has been illustratedand described in great detail inthe foregoing description, the same is to be considered as illustrativeand not restrictive in character.

The several modifications described herein, as well as others which willreadily suggest themselves, to persons skilled in this art, are allconsidered to be within the broad scope of the invention, referencebeing had to the appended claim.

The invention claimed is:

A method of obtaining flexible firing effect in a heating system havinga conventional source of heat intermittently operable in response toroom thermostat demand, a fan and motor operable at selective speeds forforcing the flow of the heating medium of the system, and a pair ofthermally responsive controls for the motor arranged for subjection totwo different thermal conditions, one thermal responsive control beingdirectly responsive to predetermined change in the active temperature ofthe heat source and the other being responsive to a predeterminedtemperature of the heating medium when subjected to the heat effect ofthe heat source, said method including automatically forcing the flow ofthe heating medium at a relatively slow rate and in response to thefirst mentioned thermal control immediately or comparatively shortlyafter room thermostat calls for h'eat, continuing that forced flowduring the heat build up period of the system until terminated by thesecond thermal control, then forcing the flow of the heating medium at amuch greater rate when the second mentioned control becomes effectiveincident to heating medium increased temperature to the predeterminedtemperature, continuing the second mentioned flow until the roomthermostat no longer calls for heat, and th'en continuing the forcedflow of the heating medium at the slower rate from immediately orcomparatively shortly after room thermostat demand is satisfied anduntil the source of heat has sufiiciently cooled as determined by thefirst mentioned control becoming ineffective for fan operation.

CHARLES H. BUCK.

